The invention relates to apparatus for towing seagoing vessels and more particularly it relates to linkages for utilization during the towing by pushing of non-propelled barges by tugboats.
In the past, non-propelled barges have been transported through the water by either "pushing" the barge from the stern by a tugboat or by "pulling" the barge at the end of a line connected to the stern of the tugboat and the bow of the barge. This application relates particularly to the former method which in the past has usually been accomplished by connecting the tugboat to the stern of a barge by a suitable linkage such as illustrated in applicant's U.S. Pat. No. 3,568,621.
Prior tugboat and barge linkages have usually allowed freedom of movement for pitching, heaving and rolling. Such movement was generally permitted because it was believed advantageous to allow the tugboat to exhibit such independent response relative to the barge. It has been found, however, that in many instances the relative rolling, i.e., independent motion around an axis along the centerline of the vessels, should be reduced to a bare minimum. When complete freedom of rolling is allowed, the tug often sustains excessive roll far beyond an acceptable range during steering.
There have been proposals to overcome the problem of relative rolling by means of a truss reinforced frame extending rearwardly from a barge and attaching directly to either side of a tugboat. Such an arrangement however requires a highly rugged construction.
It has further been proposed to provide mating surfaces between a tugboat and a barge having a stern recess to receive the bow of the tugboat as shown in applicant's U.S. Pat. No. 3,568,621, which is incorporated by reference, in order to minimize roll. While such an arrangement is effective to preclude or inhibit rolling of the tugboat relative to the barge, when the two are joined by a pivotal connection, the required surface area for the mating surfaces must be enlarged because of the many variables which determine where the sides will contact. That is, the relationship between the sides is dependant upon the pitching of the barge, the pitching of the tugboat, the pivotal motion of the linkage at the barge, whether due to heaving or pitching of either of the vessels, and the pivotal motion of the linkage at the tugboat, whether due to heaving or pitching of either of the vessels. The combination of all of these relative motions has therefore required, for example, a slot of up to eight feet in depth with a suitable matching protrusion for a tugboat-barge combination similar to that shown in applicant's patent.
Hence, to provide an improved linkage for barges and tugboats wherein it is desired to push a non-propelled barge by a tugboat, it is desirable to provide a device which eliminates the need for extended surfaces in the stern of the barge, one which provides readily defined mating surfaces, and one which minimizes strength requirements of the linkage structure.